Hi Maxime,

OK, I see that you posted questions last December and didn't seem to have the shaking, so the shaking is recent.  I am going to guess that the shaking in RA is too tight a fit of the worm against the main gear.  That might also be due to old grease.  Grease does tend to dry out over long time (years).  You mention that there is not a lot of grease on the gear.  It also depends on what kind or brand of grease is there.  Whether the old grease is the problem or not, it is probably time to re-grease your mount.  I use CMD #3 extreme pressure grease on my mount  http://www.cmdlubeoil.com/

My guess is that the tightness of the worm against the gear for a moment, then the error builds up and the servo jumps ahead.  This would occur regardless of the mount encoder setting, especially if it occurs with no mount encoder.  So this is a very important test - with the mount encoder set to IGNORE.

I could not tell from the numbers for the Renishaw what the tics/rev are.  You can read their setting using ServoConfig.exe, or read the SiTech.cfg file in a text reader like NotePad.

Don W